Whatever you may think of EVP, this is the book that started it all, way back in 1971, so at the very least it has considerable historical interest.
The
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book originally came with a record of what were claimed to be the actual examples of contact with the dead described in the text. If you'd like to hear it, listen to the last two tracks on this album:
https://archive.org/details/vvaa-an-introduction-to-evp-the-ghost-orchid-an-introduction-to-evp/78-Pista+de+audio+78.mp3